Quantization parameter signaling in video processing

ABSTRACT

The present disclosure provides methods for processing video content. One exemplary method comprises: receiving a bitstream comprising coded video data; determining a first parameter of a coding block; determining, according to the first parameter, one or more second parameters associated with a delta quantization parameter (QP) value or a chroma QP offset value; and determining, according to the one or more second parameters, at least one of the delta QP value or the chroma QP offset value.

CROSS REFERENCE TO RELATED APPLICATION

The present application is continuation of U.S. patent application Ser.No. 17/448,274, filed on Sep. 21, 2021, which is a continuation of U.S.patent application Ser. No. 16/999,730, filed on Aug. 21, 2020, whichclaims the benefits of priority to U.S. Provisional Application No.62/903,251, filed Sep. 20, 2019, all of which are incorporated herein byreference in their entireties.

TECHNICAL FIELD

The present disclosure generally relates to video processing, and moreparticularly, to methods and systems for processing video content withquantization parameters.

BACKGROUND

A video is a set of static pictures (or “frames”) capturing the visualinformation. To reduce the storage memory and the transmissionbandwidth, a video can be compressed before storage or transmission anddecompressed before display. The compression process is usually referredto as encoding and the decompression process is usually referred to asdecoding. There are various video coding formats which use standardizedvideo coding technologies, most commonly based on prediction, transform,quantization, entropy coding and in-loop filtering. The video codingstandards, such as the High Efficiency Video Coding (HEVC/H.265)standard, the Versatile Video Coding (VVC/H.266) standard AVS standards,specifying the specific video coding formats, are developed bystandardization organizations. With more and more advanced video codingtechnologies being adopted in the video standards, the coding efficiencyof the new video coding standards get higher and higher.

SUMMARY OF THE DISCLOSURE

Embodiments of the present disclosure provide a computer-implementedmethod for processing video content, including: receiving a bitstreamcomprising coded video data; determining a first parameter of a codingblock; determining, according to the first parameter, one or more secondparameters associated with a delta quantization parameter (QP) value ora chroma QP offset value; and determining, according to the one or moresecond parameters, at least one of the delta QP value or the chroma QPoffset value.

Embodiments of the present disclosure also provide a system forprocessing video content, including: a memory storing a set ofinstructions; and at least one processor configured to execute the setof instructions to cause the system to perform: receiving a bitstreamcomprising coded video data; determining a first parameter of a codingblock; determining, according to the first parameter, one or more secondparameters associated with a delta quantization parameter (QP) value ora chroma QP offset value; and determining, according to the one or moresecond parameters, at least one of the delta QP value or the chroma QPoffset value.

Embodiments of the present disclosure also provide a non-transitorycomputer readable medium storing instructions that are executable by atleast one processor of a computer system, wherein the execution of theinstructions causes the computer system to perform a method including:receiving a bitstream comprising coded video data; determining a firstparameter of a coding block; determining, according to the firstparameter, one or more second parameters associated with a deltaquantization parameter (QP) value or a chroma QP offset value; anddetermining, according to the one or more second parameters, at leastone of the delta QP value or the chroma QP offset value.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and various aspects of the present disclosure areillustrated in the following detailed description and the accompanyingfigures. Various features shown in the figures are not drawn to scale.

FIG. 1 illustrates structures of an exemplary video sequence, consistentwith embodiments of the disclosure, consistent with embodiments of thedisclosure.

FIG. 2A illustrates a schematic diagram of an exemplary encoding processof a hybrid video coding system, consistent with embodiments of thedisclosure.

FIG. 2B illustrates a schematic diagram of another exemplary encodingprocess of a hybrid video coding system, consistent with embodiments ofthe disclosure.

FIG. 3A illustrates a schematic diagram of an exemplary decoding processof a hybrid video coding system, consistent with embodiments of thedisclosure.

FIG. 3B illustrates a schematic diagram of another exemplary decodingprocess of a hybrid video coding system, consistent with embodiments ofthe disclosure.

FIG. 4 is a block diagram of an exemplary apparatus for encoding ordecoding a video, consistent with embodiments of the disclosure.

FIG. 5 illustrates an example of picture parameter sets (PPS) syntax forcoding unit (CU) delta quantization parameter (QP), consistent withembodiments of the disclosure.

FIG. 6 illustrates an example of coding tree level syntax for CU deltaQP, consistent with embodiments of the disclosure.

FIG. 7 illustrates an example of transform unit level syntax for CUdelta QP, consistent with embodiments of the disclosure.

FIG. 8 illustrates an example of slice header syntax, consistent withembodiments of the disclosure.

FIG. 9 illustrates another example of slice header syntax, consistentwith embodiments of the disclosure.

FIG. 10 illustrates yet another example of slice header syntax,consistent with embodiments of the disclosure.

FIG. 11 illustrates another example of picture header syntax, consistentwith embodiments of the disclosure.

FIG. 12 illustrates an example of PPS syntax for cu_qp_delta_subdiv andcu_chroma_qp_offset_subdiv, consistent with embodiments of thedisclosure.

FIG. 13 illustrates an example of slice header syntax forcu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv, consistent withembodiments of the disclosure.

FIG. 14 illustrates an example of syntax for sps_max_mtt_depth_luma,consistent with embodiments of the disclosure.

FIG. 15 illustrates an example of syntax for pps_max_mtt_depth_luma,consistent with embodiments of the disclosure.

FIG. 16 illustrates an example of SPS syntax for cu_qp_delta_subdiv andcu_chroma_qp_offset_subdiv, consistent with embodiments of thedisclosure.

FIG. 17 illustrates an example of slice header syntax forcu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv, consistent withembodiments of the disclosure.

FIG. 18 illustrates an example of syntax for sps_max_mtt_depth_luma,consistent with embodiments of the disclosure.

FIG. 19 illustrates another example of syntax forsps_max_mtt_depth_luma, consistent with embodiments of the disclosure.

FIG. 20 illustrates an example of syntax for pps_max_mtt_depth_luma,consistent with embodiments of the disclosure.

FIG. 21 is a flowchart of an exemplary computer-implemented method forprocessing video content, consistent with embodiments of the disclosure.

DETAILED DESCRIPTION

Video coding systems are often used to compress digital video signals,for instance to reduce storage space consumed or to reduce transmissionbandwidth consumption associated with such signals. With high-definition(HD) videos (e.g., having a resolution of 1920×1080 pixels) gainingpopularity in various applications of video compression, such as onlinevideo streaming, video conferencing, or video monitoring, it is acontinuous need to develop video coding tools that can increasecompression efficiency of video data.

For example, video monitoring applications are increasingly andextensively used in many application scenarios (e.g., security, traffic,environment monitoring, or the like), and the numbers and resolutions ofthe monitoring devices keep growing rapidly. Many video monitoringapplication scenarios prefer to provide HD videos to users to capturemore information, which has more pixels per frame to capture suchinformation. However, an HD video bitstream can have a high bitrate thatdemands high bandwidth for transmission and large space for storage. Forexample, a monitoring video stream having an average 1920×1080resolution can require a bandwidth as high as 4 Mbps for real-timetransmission. Also, the video monitoring generally monitors 7×24continuously, which can greatly challenge a storage system, if the videodata is to be stored. The demand for high bandwidth and large storage ofthe HD videos has therefore become a major limitation to its large-scaledeployment in video monitoring.

A video is a set of static pictures (or “frames”) arranged in a temporalsequence to store visual information. A video capture device (e.g., acamera) can be used to capture and store those pictures in a temporalsequence, and a video playback device (e.g., a television, a computer, asmartphone, a tablet computer, a video player, or any end-user terminalwith a function of display) can be used to display such pictures in thetemporal sequence. Also, in some applications, a video capturing devicecan transmit the captured video to the video playback device (e.g., acomputer with a monitor) in real-time, such as for monitoring,conferencing, or live broadcasting.

For reducing the storage space and the transmission bandwidth needed bysuch applications, the video can be compressed before storage andtransmission and decompressed before the display. The compression anddecompression can be implemented by software executed by a processor(e.g., a processor of a generic computer) or specialized hardware. Themodule for compression is generally referred to as an “encoder,” and themodule for decompression is generally referred to as a “decoder.” Theencoder and decoder can be collectively referred to as a “codec.” Theencoder and decoder can be implemented as any of a variety of suitablehardware, software, or a combination thereof. For example, the hardwareimplementation of the encoder and decoder can include circuitry, such asone or more microprocessors, digital signal processors (DSPs),application-specific integrated circuits (ASICs), field-programmablegate arrays (FPGAs), discrete logic, or any combinations thereof. Thesoftware implementation of the encoder and decoder can include programcodes, computer-executable instructions, firmware, or any suitablecomputer-implemented algorithm or process fixed in a computer-readablemedium. Video compression and decompression can be implemented byvarious algorithms or standards, such as MPEG-1, MPEG-2, MPEG-4, H.26xseries, or the like. In some applications, the codec can decompress thevideo from a first coding standard and re-compress the decompressedvideo using a second coding standard, in which case the codec can bereferred to as a “transcoder.”

The video encoding process can identify and keep useful information thatcan be used to reconstruct a picture and disregard unimportantinformation for the reconstruction. If the disregarded, unimportantinformation cannot be fully reconstructed, such an encoding process canbe referred to as “lossy.” Otherwise, it can be referred to as“lossless.” Most encoding processes are lossy, which is a tradeoff toreduce the needed storage space and the transmission bandwidth.

The useful information of a picture being encoded (referred to as a“current picture”) include changes with respect to a reference picture(e.g., a picture previously encoded and reconstructed). Such changes caninclude position changes, luminosity changes, or color changes of thepixels, among which the position changes are mostly concerned. Positionchanges of a group of pixels that represent an object can reflect themotion of the object between the reference picture and the currentpicture.

A picture coded without referencing another picture (i.e., it is its ownreference picture) is referred to as an “I-picture.” A picture codedusing a previous picture as a reference picture is referred to as a“P-picture.” A picture coded using both a previous picture and a futurepicture as reference pictures (i.e., the reference is “bi-directional”)is referred to as a “B-picture.”

As previously mentioned, video monitoring that uses HD videos faceschallenges of demands of high bandwidth and large storage. Foraddressing such challenges, the bitrate of the encoded video can bereduced. Among the I-, P-, and B-pictures, I-pictures have the highestbitrate. Because the backgrounds of most monitoring videos are nearlystatic, one way to reduce the overall bitrate of the encoded video canbe using fewer I-pictures for video encoding.

However, the improvement of using fewer I-pictures can be trivialbecause the I-pictures are typically not dominant in the encoded video.For example, in a typical video bitstream, the ratio of I-, B-, andP-pictures can be 1:20:9, in which the I-pictures can account for lessthan 10% of the total bitrate. In other words, in such an example, evenall I-pictures are removed, the reduced bitrate can be no more than 10%.

This disclosure provides methods, apparatuses, and systems forprocessing video content using adaptive resolution change (ARC). Unlikeinaccurate phases caused by phase rounding, embodiments of thedisclosure provide a pixel refinement process based on a fixed-phaseinterpolation to reduce the complexity of the algorithm and the hardwarewhile maintain accuracy.

FIG. 1 illustrates structures of an example video sequence 100,consistent with embodiments of the disclosure. Video sequence 100 can bea live video or a video having been captured and archived. Video 100 canbe a real-life video, a computer-generated video (e.g., computer gamevideo), or a combination thereof (e.g., a real-life video withaugmented-reality effects). Video sequence 100 can be inputted from avideo capture device (e.g., a camera), a video archive (e.g., a videofile stored in a storage device) containing previously captured video,or a video feed interface (e.g., a video broadcast transceiver) toreceive video from a video content provider.

As shown in FIG. 1 , video sequence 100 can include a series of picturesarranged temporally along a timeline, including pictures 102, 104, 106,and 108. Pictures 102-106 are continuous, and there are more picturesbetween pictures 106 and 108. In FIG. 1 , picture 102 is an I-picture,the reference picture of which is picture 102 itself. Picture 104 is aP-picture, the reference picture of which is picture 102, as indicatedby the arrow. Picture 106 is a B-picture, the reference pictures ofwhich are pictures 104 and 108, as indicated by the arrows. In someembodiments, the reference picture of a picture (e.g., picture 104) canbe not immediately preceding or following the picture. For example, thereference picture of picture 104 can be a picture preceding picture 102.It should be noted that the reference pictures of pictures 102-106 areonly examples, and this disclosure does not limit embodiments of thereference pictures as the examples shown in FIG. 1 .

Typically, video codecs do not encode or decode an entire picture at onetime due to the computing complexity of such tasks. Rather, they cansplit the picture into basic segments, and encode or decode the picturesegment by segment. Such basic segments are referred to as basicprocessing units (“BPUs”) in this disclosure. For example, structure 110in FIG. 1 shows an example structure of a picture of video sequence 100(e.g., any of pictures 102-108). In structure 110, a picture is dividedinto 4×4 basic processing units, the boundaries of which are shown asdash lines. In some embodiments, the basic processing units can bereferred to as “macroblocks” in some video coding standards (e.g., MPEGfamily, H.261, H.263, or H.264/AVC), or as “coding tree units” (“CTUs”)in some other video coding standards (e.g., H.265/HEVC or H.266/VVC).The basic processing units can have variable sizes in a picture, such as128×128, 64×64, 32×32, 16×16, 4×8, 16×32, or any arbitrary shape andsize of pixels. The sizes and shapes of the basic processing units canbe selected for a picture based on the balance of coding efficiency andlevels of details to be kept in the basic processing unit.

The basic processing units can be logical units, which can include agroup of different types of video data stored in a computer memory(e.g., in a video frame buffer). For example, a basic processing unit ofa color picture can include a luma component (Y) representing achromaticbrightness information, one or more chroma components (e.g., Cb and Cr)representing color information, and associated syntax elements, in whichthe luma and chroma components can have the same size of the basicprocessing unit. The luma and chroma components can be referred to as“coding tree blocks” (“CTBs”) in some video coding standards (e.g.,H.265/HEVC or H.266/VVC). Any operation performed to a basic processingunit can be repeatedly performed to each of its luma and chromacomponents.

Video coding has multiple stages of operations, examples of which willbe detailed in FIGS. 2A-2B and 3A-3B. For each stage, the size of thebasic processing units can still be too large for processing, and thuscan be further divided into segments referred to as “basic processingsub-units” in this disclosure. In some embodiments, the basic processingsub-units can be referred to as “blocks” in some video coding standards(e.g., MPEG family, H.261, H.263, or H.264/AVC), or as “coding units”(“CUs”) in some other video coding standards (e.g., H.265/HEVC orH.266/VVC). A basic processing sub-unit can have the same or smallersize than the basic processing unit. Similar to the basic processingunits, basic processing sub-units are also logical units, which caninclude a group of different types of video data (e.g., Y, Cb, Cr, andassociated syntax elements) stored in a computer memory (e.g., in avideo frame buffer). Any operation performed to a basic processingsub-unit can be repeatedly performed to each of its luma and chromacomponents. It should be noted that such division can be performed tofurther levels depending on processing needs. It should also be notedthat different stages can divide the basic processing units usingdifferent schemes.

For example, at a mode decision stage (an example of which will bedetailed in FIG. 2B), the encoder can decide what prediction mode (e.g.,intra-picture prediction or inter-picture prediction) to use for a basicprocessing unit, which can be too large to make such a decision. Theencoder can split the basic processing unit into multiple basicprocessing sub-units (e.g., CUs as in H.265/HEVC or H.266/VVC), anddecide a prediction type for each individual basic processing sub-unit.

For another example, at a prediction stage (an example of which will bedetailed in FIG. 2A), the encoder can perform prediction operation atthe level of basic processing sub-units (e.g., CUs). However, in somecases, a basic processing sub-unit can still be too large to process.The encoder can further split the basic processing sub-unit into smallersegments (e.g., referred to as “prediction blocks” or “PBs” inH.265/HEVC or H.266/VVC), at the level of which the prediction operationcan be performed.

For another example, at a transform stage (an example of which will bedetailed in FIG. 2A), the encoder can perform a transform operation forresidual basic processing sub-units (e.g., CUs). However, in some cases,a basic processing sub-unit can still be too large to process. Theencoder can further split the basic processing sub-unit into smallersegments (e.g., referred to as “transform blocks” or “TBs” in H.265/HEVCor H.266/VVC), at the level of which the transform operation can beperformed. It should be noted that the division schemes of the samebasic processing sub-unit can be different at the prediction stage andthe transform stage. For example, in H.265/HEVC or H.266/VVC, theprediction blocks and transform blocks of the same CU can have differentsizes and numbers.

In structure 110 of FIG. 1 , basic processing unit 112 is furtherdivided into 3×3 basic processing sub-units, the boundaries of which areshown as dotted lines. Different basic processing units of the samepicture can be divided into basic processing sub-units in differentschemes.

In some implementations, to provide the capability of parallelprocessing and error resilience to video encoding and decoding, apicture can be divided into regions for processing, such that, for aregion of the picture, the encoding or decoding process can depend on noinformation from any other region of the picture. In other words, eachregion of the picture can be processed independently. By doing so, thecodec can process different regions of a picture in parallel, thusincreasing the coding efficiency. Also, when data of a region iscorrupted in the processing or lost in network transmission, the codeccan correctly encode or decode other regions of the same picture withoutreliance on the corrupted or lost data, thus providing the capability oferror resilience. In some video coding standards, a picture can bedivided into different types of regions. For example, H.265/HEVC andH.266/VVC provide two types of regions: “slices” and “tiles.” It shouldalso be noted that different pictures of video sequence 100 can havedifferent partition schemes for dividing a picture into regions.

For example, in FIG. 1 , structure 110 is divided into three regions114, 116, and 118, the boundaries of which are shown as solid linesinside structure 110. Region 114 includes four basic processing units.Each of regions 116 and 118 includes six basic processing units. Itshould be noted that the basic processing units, basic processingsub-units, and regions of structure 110 in FIG. 1 are only examples, andthis disclosure does not limit embodiments thereof.

FIG. 2A illustrates a schematic diagram of an example encoding process200A, consistent with embodiments of the disclosure. An encoder canencode video sequence 202 into video bitstream 228 according to process200A. Similar to video sequence 100 in FIG. 1 , video sequence 202 caninclude a set of pictures (referred to as “original pictures”) arrangedin a temporal order. Similar to structure 110 in FIG. 1 , each originalpicture of video sequence 202 can be divided by the encoder into basicprocessing units, basic processing sub-units, or regions for processing.In some embodiments, the encoder can perform process 200A at the levelof basic processing units for each original picture of video sequence202. For example, the encoder can perform process 200A in an iterativemanner, in which the encoder can encode a basic processing unit in oneiteration of process 200A. In some embodiments, the encoder can performprocess 200A in parallel for regions (e.g., regions 114-118) of eachoriginal picture of video sequence 202.

In FIG. 2A, the encoder can feed a basic processing unit (referred to asan “original BPU”) of an original picture of video sequence 202 toprediction stage 204 to generate prediction data 206 and predicted BPU208. The encoder can subtract predicted BPU 208 from the original BPU togenerate residual BPU 210. The encoder can feed residual BPU 210 totransform stage 212 and quantization stage 214 to generate quantizedtransform coefficients 216. The encoder can feed prediction data 206 andquantized transform coefficients 216 to binary coding stage 226 togenerate video bitstream 228. Components 202, 204, 206, 208, 210, 212,214, 216, 226, and 228 can be referred to as a “forward path.” Duringprocess 200A, after quantization stage 214, the encoder can feedquantized transform coefficients 216 to inverse quantization stage 218and inverse transform stage 220 to generate reconstructed residual BPU222. The encoder can add reconstructed residual BPU 222 to predicted BPU208 to generate prediction reference 224, which is used in predictionstage 204 for the next iteration of process 200A. Components 218, 220,222, and 224 of process 200A can be referred to as a “reconstructionpath.” The reconstruction path can be used to ensure that both theencoder and the decoder use the same reference data for prediction.

The encoder can perform process 200A iteratively to encode each originalBPU of the original picture (in the forward path) and generate predictedreference 224 for encoding the next original BPU of the original picture(in the reconstruction path). After encoding all original BPUs of theoriginal picture, the encoder can proceed to encode the next picture invideo sequence 202.

Referring to process 200A, the encoder can receive video sequence 202generated by a video capturing device (e.g., a camera). The term“receive” used herein can refer to receiving, inputting, acquiring,retrieving, obtaining, reading, accessing, or any action in any mannerfor inputting data.

At prediction stage 204, at a current iteration, the encoder can receivean original BPU and prediction reference 224, and perform a predictionoperation to generate prediction data 206 and predicted BPU 208.Prediction reference 224 can be generated from the reconstruction pathof the previous iteration of process 200A. The purpose of predictionstage 204 is to reduce information redundancy by extracting predictiondata 206 that can be used to reconstruct the original BPU as predictedBPU 208 from prediction data 206 and prediction reference 224.

Ideally, predicted BPU 208 can be identical to the original BPU.However, due to non-ideal prediction and reconstruction operations,predicted BPU 208 is generally slightly different from the original BPU.For recording such differences, after generating predicted BPU 208, theencoder can subtract it from the original BPU to generate residual BPU210. For example, the encoder can subtract values (e.g., greyscalevalues or RGB values) of pixels of predicted BPU 208 from values ofcorresponding pixels of the original BPU. Each pixel of residual BPU 210can have a residual value as a result of such subtraction between thecorresponding pixels of the original BPU and predicted BPU 208. Comparedwith the original BPU, prediction data 206 and residual BPU 210 can havefewer bits, but they can be used to reconstruct the original BPU withoutsignificant quality deterioration. Thus, the original BPU is compressed.

To further compress residual BPU 210, at transform stage 212, theencoder can reduce spatial redundancy of residual BPU 210 by decomposingit into a set of two-dimensional “base patterns,” each base patternbeing associated with a “transform coefficient.” The base patterns canhave the same size (e.g., the size of residual BPU 210). Each basepattern can represent a variation frequency (e.g., frequency ofbrightness variation) component of residual BPU 210. None of the basepatterns can be reproduced from any combinations (e.g., linearcombinations) of any other base patterns. In other words, thedecomposition can decompose variations of residual BPU 210 into afrequency domain. Such a decomposition is analogous to a discreteFourier transform of a function, in which the base patterns areanalogous to the base functions (e.g., trigonometry functions) of thediscrete Fourier transform, and the transform coefficients are analogousto the coefficients associated with the base functions.

Different transform algorithms can use different base patterns. Varioustransform algorithms can be used at transform stage 212, such as, forexample, a discrete cosine transform, a discrete sine transform, or thelike. The transform at transform stage 212 is invertible. That is, theencoder can restore residual BPU 210 by an inverse operation of thetransform (referred to as an “inverse transform”). For example, torestore a pixel of residual BPU 210, the inverse transform can bemultiplying values of corresponding pixels of the base patterns byrespective associated coefficients and adding the products to produce aweighted sum. For a video coding standard, both the encoder and decodercan use the same transform algorithm (thus the same base patterns).Thus, the encoder can record only the transform coefficients, from whichthe decoder can reconstruct residual BPU 210 without receiving the basepatterns from the encoder. Compared with residual BPU 210, the transformcoefficients can have fewer bits, but they can be used to reconstructresidual BPU 210 without significant quality deterioration. Thus,residual BPU 210 is further compressed.

The encoder can further compress the transform coefficients atquantization stage 214. In the transform process, different basepatterns can represent different variation frequencies (e.g., brightnessvariation frequencies). Because human eyes are generally better atrecognizing low-frequency variation, the encoder can disregardinformation of high-frequency variation without causing significantquality deterioration in decoding. For example, at quantization stage214, the encoder can generate quantized transform coefficients 216 bydividing each transform coefficient by an integer value (referred to asa “quantization parameter”) and rounding the quotient to its nearestinteger. After such an operation, some transform coefficients of thehigh-frequency base patterns can be converted to zero, and the transformcoefficients of the low-frequency base patterns can be converted tosmaller integers. The encoder can disregard the zero-value quantizedtransform coefficients 216, by which the transform coefficients arefurther compressed. The quantization process is also invertible, inwhich quantized transform coefficients 216 can be reconstructed to thetransform coefficients in an inverse operation of the quantization(referred to as “inverse quantization”).

Because the encoder disregards the remainders of such divisions in therounding operation, quantization stage 214 can be lossy. Typically,quantization stage 214 can contribute the most information loss inprocess 200A. The larger the information loss is, the fewer bits thequantized transform coefficients 216 can need. For obtaining differentlevels of information loss, the encoder can use different values of thequantization parameter or any other parameter of the quantizationprocess.

At binary coding stage 226, the encoder can encode prediction data 206and quantized transform coefficients 216 using a binary codingtechnique, such as, for example, entropy coding, variable length coding,arithmetic coding, Huffman coding, context-adaptive binary arithmeticcoding, or any other lossless or lossy compression algorithm. In someembodiments, besides prediction data 206 and quantized transformcoefficients 216, the encoder can encode other information at binarycoding stage 226, such as, for example, a prediction mode used atprediction stage 204, parameters of the prediction operation, atransform type at transform stage 212, parameters of the quantizationprocess (e.g., quantization parameters), an encoder control parameter(e.g., a bitrate control parameter), or the like. The encoder can usethe output data of binary coding stage 226 to generate video bitstream228. In some embodiments, video bitstream 228 can be further packetizedfor network transmission.

Referring to the reconstruction path of process 200A, at inversequantization stage 218, the encoder can perform inverse quantization onquantized transform coefficients 216 to generate reconstructed transformcoefficients. At inverse transform stage 220, the encoder can generatereconstructed residual BPU 222 based on the reconstructed transformcoefficients. The encoder can add reconstructed residual BPU 222 topredicted BPU 208 to generate prediction reference 224 that is to beused in the next iteration of process 200A.

It should be noted that other variations of the process 200A can be usedto encode video sequence 202. In some embodiments, stages of process200A can be performed by the encoder in different orders. In someembodiments, one or more stages of process 200A can be combined into asingle stage. In some embodiments, a single stage of process 200A can bedivided into multiple stages. For example, transform stage 212 andquantization stage 214 can be combined into a single stage. In someembodiments, process 200A can include additional stages. In someembodiments, process 200A can omit one or more stages in FIG. 2A.

FIG. 2B illustrates a schematic diagram of another example encodingprocess 200B, consistent with embodiments of the disclosure. Process200B can be modified from process 200A. For example, process 200B can beused by an encoder conforming to a hybrid video coding standard (e.g.,H.26x series). Compared with process 200A, the forward path of process200B additionally includes mode decision stage 230 and dividesprediction stage 204 into spatial prediction stage 2042 and temporalprediction stage 2044. The reconstruction path of process 200Badditionally includes loop filter stage 232 and buffer 234.

Generally, prediction techniques can be categorized into two types:spatial prediction and temporal prediction. Spatial prediction (e.g., anintra-picture prediction or “intra prediction”) can use pixels from oneor more already coded neighboring BPUs in the same picture to predictthe current BPU. That is, prediction reference 224 in the spatialprediction can include the neighboring BPUs. The spatial prediction canreduce the inherent spatial redundancy of the picture. Temporalprediction (e.g., an inter-picture prediction or “inter prediction”) canuse regions from one or more already coded pictures to predict thecurrent BPU. That is, prediction reference 224 in the temporalprediction can include the coded pictures. The temporal prediction canreduce the inherent temporal redundancy of the pictures.

Referring to process 200B, in the forward path, the encoder performs theprediction operation at spatial prediction stage 2042 and temporalprediction stage 2044. For example, at spatial prediction stage 2042,the encoder can perform the intra prediction. For an original BPU of apicture being encoded, prediction reference 224 can include one or moreneighboring BPUs that have been encoded (in the forward path) andreconstructed (in the reconstructed path) in the same picture. Theencoder can generate predicted BPU 208 by extrapolating the neighboringBPUs. The extrapolation technique can include, for example, a linearextrapolation or interpolation, a polynomial extrapolation orinterpolation, or the like. In some embodiments, the encoder can performthe extrapolation at the pixel level, such as by extrapolating values ofcorresponding pixels for each pixel of predicted BPU 208. Theneighboring BPUs used for extrapolation can be located with respect tothe original BPU from various directions, such as in a verticaldirection (e.g., on top of the original BPU), a horizontal direction(e.g., to the left of the original BPU), a diagonal direction (e.g., tothe down-left, down-right, up-left, or up-right of the original BPU), orany direction defined in the used video coding standard. For the intraprediction, prediction data 206 can include, for example, locations(e.g., coordinates) of the used neighboring BPUs, sizes of the usedneighboring BPUs, parameters of the extrapolation, a direction of theused neighboring BPUs with respect to the original BPU, or the like.

For another example, at temporal prediction stage 2044, the encoder canperform the inter prediction. For an original BPU of a current picture,prediction reference 224 can include one or more pictures (referred toas “reference pictures”) that have been encoded (in the forward path)and reconstructed (in the reconstructed path). In some embodiments, areference picture can be encoded and reconstructed BPU by BPU. Forexample, the encoder can add reconstructed residual BPU 222 to predictedBPU 208 to generate a reconstructed BPU. When all reconstructed BPUs ofthe same picture are generated, the encoder can generate a reconstructedpicture as a reference picture. The encoder can perform an operation of“motion estimation” to search for a matching region in a scope (referredto as a “search window”) of the reference picture. The location of thesearch window in the reference picture can be determined based on thelocation of the original BPU in the current picture. For example, thesearch window can be centered at a location having the same coordinatesin the reference picture as the original BPU in the current picture andcan be extended out for a predetermined distance. When the encoderidentifies (e.g., by using a pel-recursive algorithm, a block-matchingalgorithm, or the like) a region similar to the original BPU in thesearch window, the encoder can determine such a region as the matchingregion. The matching region can have different dimensions (e.g., beingsmaller than, equal to, larger than, or in a different shape) from theoriginal BPU. Because the reference picture and the current picture aretemporally separated in the timeline (e.g., as shown in FIG. 1 ), it canbe deemed that the matching region “moves” to the location of theoriginal BPU as time goes by. The encoder can record the direction anddistance of such a motion as a “motion vector.” When multiple referencepictures are used (e.g., as picture 106 in FIG. 1 ), the encoder cansearch for a matching region and determine its associated motion vectorfor each reference picture. In some embodiments, the encoder can assignweights to pixel values of the matching regions of respective matchingreference pictures.

The motion estimation can be used to identify various types of motions,such as, for example, translations, rotations, zooming, or the like. Forinter prediction, prediction data 206 can include, for example,locations (e.g., coordinates) of the matching region, the motion vectorsassociated with the matching region, the number of reference pictures,weights associated with the reference pictures, or the like.

For generating predicted BPU 208, the encoder can perform an operationof “motion compensation.” The motion compensation can be used toreconstruct predicted BPU 208 based on prediction data 206 (e.g., themotion vector) and prediction reference 224. For example, the encodercan move the matching region of the reference picture according to themotion vector, in which the encoder can predict the original BPU of thecurrent picture. When multiple reference pictures are used (e.g., aspicture 106 in FIG. 1 ), the encoder can move the matching regions ofthe reference pictures according to the respective motion vectors andaverage pixel values of the matching regions. In some embodiments, ifthe encoder has assigned weights to pixel values of the matching regionsof respective matching reference pictures, the encoder can add aweighted sum of the pixel values of the moved matching regions.

In some embodiments, the inter prediction can be unidirectional orbidirectional. Unidirectional inter predictions can use one or morereference pictures in the same temporal direction with respect to thecurrent picture. For example, picture 104 in FIG. 1 is a unidirectionalinter-predicted picture, in which the reference picture (i.e., picture102) precedes picture 104. Bidirectional inter predictions can use oneor more reference pictures at both temporal directions with respect tothe current picture. For example, picture 106 in FIG. 1 is abidirectional inter-predicted picture, in which the reference pictures(i.e., pictures 104 and 108) are at both temporal directions withrespect to picture 104.

Still referring to the forward path of process 200B, after spatialprediction 2042 and temporal prediction stage 2044, at mode decisionstage 230, the encoder can select a prediction mode (e.g., one of theintra prediction or the inter prediction) for the current iteration ofprocess 200B. For example, the encoder can perform a rate-distortionoptimization technique, in which the encoder can select a predictionmode to minimize a value of a cost function depending on a bit rate of acandidate prediction mode and distortion of the reconstructed referencepicture under the candidate prediction mode. Depending on the selectedprediction mode, the encoder can generate the corresponding predictedBPU 208 and predicted data 206.

In the reconstruction path of process 200B, if intra prediction mode hasbeen selected in the forward path, after generating prediction reference224 (e.g., the current BPU that has been encoded and reconstructed inthe current picture), the encoder can directly feed prediction reference224 to spatial prediction stage 2042 for later usage (e.g., forextrapolation of a next BPU of the current picture). If the interprediction mode has been selected in the forward path, after generatingprediction reference 224 (e.g., the current picture in which all BPUshave been encoded and reconstructed), the encoder can feed predictionreference 224 to loop filter stage 232, at which the encoder can apply aloop filter to prediction reference 224 to reduce or eliminatedistortion (e.g., blocking artifacts) introduced by the interprediction. The encoder can apply various loop filter techniques at loopfilter stage 232, such as, for example, deblocking, sample adaptiveoffsets, adaptive loop filters, or the like. The loop-filtered referencepicture can be stored in buffer 234 (or “decoded picture buffer”) forlater use (e.g., to be used as an inter-prediction reference picture fora future picture of video sequence 202). The encoder can store one ormore reference pictures in buffer 234 to be used at temporal predictionstage 2044. In some embodiments, the encoder can encode parameters ofthe loop filter (e.g., a loop filter strength) at binary coding stage226, along with quantized transform coefficients 216, prediction data206, and other information.

FIG. 3A illustrates a schematic diagram of an example decoding process300A, consistent with embodiments of the disclosure. Process 300A can bea decompression process corresponding to the compression process 200A inFIG. 2A. In some embodiments, process 300A can be similar to thereconstruction path of process 200A. A decoder can decode videobitstream 228 into video stream 304 according to process 300A. Videostream 304 can be very similar to video sequence 202. However, due tothe information loss in the compression and decompression process (e.g.,quantization stage 214 in FIGS. 2A-2B), generally, video stream 304 isnot identical to video sequence 202. Similar to processes 200A and 200Bin FIGS. 2A-2B, the decoder can perform process 300A at the level ofbasic processing units (BPUs) for each picture encoded in videobitstream 228. For example, the decoder can perform process 300A in aniterative manner, in which the decoder can decode a basic processingunit in one iteration of process 300A. In some embodiments, the decodercan perform process 300A in parallel for regions (e.g., regions 114-118)of each picture encoded in video bitstream 228.

In FIG. 3A, the decoder can feed a portion of video bitstream 228associated with a basic processing unit (referred to as an “encodedBPU”) of an encoded picture to binary decoding stage 302. At binarydecoding stage 302, the decoder can decode the portion into predictiondata 206 and quantized transform coefficients 216. The decoder can feedquantized transform coefficients 216 to inverse quantization stage 218and inverse transform stage 220 to generate reconstructed residual BPU222. The decoder can feed prediction data 206 to prediction stage 204 togenerate predicted BPU 208. The decoder can add reconstructed residualBPU 222 to predicted BPU 208 to generate predicted reference 224. Insome embodiments, predicted reference 224 can be stored in a buffer(e.g., a decoded picture buffer in a computer memory). The decoder canfeed predicted reference 224 to prediction stage 204 for performing aprediction operation in the next iteration of process 300A.

The decoder can perform process 300A iteratively to decode each encodedBPU of the encoded picture and generate predicted reference 224 forencoding the next encoded BPU of the encoded picture. After decoding allencoded BPUs of the encoded picture, the decoder can output the pictureto video stream 304 for display and proceed to decode the next encodedpicture in video bitstream 228.

At binary decoding stage 302, the decoder can perform an inverseoperation of the binary coding technique used by the encoder (e.g.,entropy coding, variable length coding, arithmetic coding, Huffmancoding, context-adaptive binary arithmetic coding, or any other losslesscompression algorithm). In some embodiments, besides prediction data 206and quantized transform coefficients 216, the decoder can decode otherinformation at binary decoding stage 302, such as, for example, aprediction mode, parameters of the prediction operation, a transformtype, parameters of the quantization process (e.g., quantizationparameters), an encoder control parameter (e.g., a bitrate controlparameter), or the like. In some embodiments, if video bitstream 228 istransmitted over a network in packets, the decoder can depacketize videobitstream 228 before feeding it to binary decoding stage 302.

FIG. 3B illustrates a schematic diagram of another example decodingprocess 300B, consistent with embodiments of the disclosure. Process300B can be modified from process 300A. For example, process 300B can beused by a decoder conforming to a hybrid video coding standard (e.g.,H.26x series). Compared with process 300A, process 300B additionallydivides prediction stage 204 into spatial prediction stage 2042 andtemporal prediction stage 2044, and additionally includes loop filterstage 232 and buffer 234.

In process 300B, for an encoded basic processing unit (referred to as a“current BPU”) of an encoded picture (referred to as a “currentpicture”) that is being decoded, prediction data 206 decoded from binarydecoding stage 302 by the decoder can include various types of data,depending on what prediction mode was used to encode the current BPU bythe encoder. For example, if intra prediction was used by the encoder toencode the current BPU, prediction data 206 can include a predictionmode indicator (e.g., a flag value) indicative of the intra prediction,parameters of the intra prediction operation, or the like. Theparameters of the intra prediction operation can include, for example,locations (e.g., coordinates) of one or more neighboring BPUs used as areference, sizes of the neighboring BPUs, parameters of extrapolation, adirection of the neighboring BPUs with respect to the original BPU, orthe like. For another example, if inter prediction was used by theencoder to encode the current BPU, prediction data 206 can include aprediction mode indicator (e.g., a flag value) indicative of the interprediction, parameters of the inter prediction operation, or the like.The parameters of the inter prediction operation can include, forexample, the number of reference pictures associated with the currentBPU, weights respectively associated with the reference pictures,locations (e.g., coordinates) of one or more matching regions in therespective reference pictures, one or more motion vectors respectivelyassociated with the matching regions, or the like.

Based on the prediction mode indicator, the decoder can decide whetherto perform a spatial prediction (e.g., the intra prediction) at spatialprediction stage 2042 or a temporal prediction (e.g., the interprediction) at temporal prediction stage 2044. The details of performingsuch spatial prediction or temporal prediction are described in FIG. 2Band will not be repeated hereinafter. After performing such spatialprediction or temporal prediction, the decoder can generate predictedBPU 208. The decoder can add predicted BPU 208 and reconstructedresidual BPU 222 to generate prediction reference 224, as described inFIG. 3A.

In process 300B, the decoder can feed predicted reference 224 to spatialprediction stage 2042 or temporal prediction stage 2044 for performing aprediction operation in the next iteration of process 300B. For example,if the current BPU is decoded using the intra prediction at spatialprediction stage 2042, after generating prediction reference 224 (e.g.,the decoded current BPU), the decoder can directly feed predictionreference 224 to spatial prediction stage 2042 for later usage (e.g.,for extrapolation of a next BPU of the current picture). If the currentBPU is decoded using the inter prediction at temporal prediction stage2044, after generating prediction reference 224 (e.g., a referencepicture in which all BPUs have been decoded), the encoder can feedprediction reference 224 to loop filter stage 232 to reduce or eliminatedistortion (e.g., blocking artifacts). The decoder can apply a loopfilter to prediction reference 224, in a way as described in FIG. 2B.The loop-filtered reference picture can be stored in buffer 234 (e.g., adecoded picture buffer in a computer memory) for later use (e.g., to beused as an inter-prediction reference picture for a future encodedpicture of video bitstream 228). The decoder can store one or morereference pictures in buffer 234 to be used at temporal prediction stage2044. In some embodiments, when the prediction mode indicator ofprediction data 206 indicates that inter prediction was used to encodethe current BPU, prediction data can further include parameters of theloop filter (e.g., a loop filter strength).

FIG. 4 is a block diagram of an example apparatus 400 for encoding ordecoding a video, consistent with embodiments of the disclosure. Asshown in FIG. 4 , apparatus 400 can include processor 402. Whenprocessor 402 executes instructions described herein, apparatus 400 canbecome a specialized machine for video encoding or decoding. Processor402 can be any type of circuitry capable of manipulating or processinginformation. For example, processor 402 can include any combination ofany number of a central processing unit (or “CPU”), a graphicsprocessing unit (or “GPU”), a neural processing unit (“NPU”), amicrocontroller unit (“MCU”), an optical processor, a programmable logiccontroller, a microcontroller, a microprocessor, a digital signalprocessor, an intellectual property (IP) core, a Programmable LogicArray (PLA), a Programmable Array Logic (PAL), a Generic Array Logic(GAL), a Complex Programmable Logic Device (CPLD), a Field-ProgrammableGate Array (FPGA), a System On Chip (SoC), an Application-SpecificIntegrated Circuit (ASIC), or the like. In some embodiments, processor402 can also be a set of processors grouped as a single logicalcomponent. For example, as shown in FIG. 4 , processor 402 can includemultiple processors, including processor 402 a, processor 402 b, andprocessor 402 n.

Apparatus 400 can also include memory 404 configured to store data(e.g., a set of instructions, computer codes, intermediate data, or thelike). For example, as shown in FIG. 4 , the stored data can includeprogram instructions (e.g., program instructions for implementing thestages in processes 200A, 200B, 300A, or 300B) and data for processing(e.g., video sequence 202, video bitstream 228, or video stream 304).Processor 402 can access the program instructions and data forprocessing (e.g., via bus 410), and execute the program instructions toperform an operation or manipulation on the data for processing. Memory404 can include a high-speed random-access storage device or anon-volatile storage device. In some embodiments, memory 404 can includeany combination of any number of a random-access memory (RAM), aread-only memory (ROM), an optical disc, a magnetic disk, a hard drive,a solid-state drive, a flash drive, a security digital (SD) card, amemory stick, a compact flash (CF) card, or the like. Memory 404 canalso be a group of memories (not shown in FIG. 4 ) grouped as a singlelogical component.

Bus 410 can be a communication device that transfers data betweencomponents inside apparatus 400, such as an internal bus (e.g., aCPU-memory bus), an external bus (e.g., a universal serial bus port, aperipheral component interconnect express port), or the like.

For ease of explanation without causing ambiguity, processor 402 andother data processing circuits are collectively referred to as a “dataprocessing circuit” in this disclosure. The data processing circuit canbe implemented entirely as hardware, or as a combination of software,hardware, or firmware. In addition, the data processing circuit can be asingle independent module or can be combined entirely or partially intoany other component of apparatus 400.

Apparatus 400 can further include network interface 406 to provide wiredor wireless communication with a network (e.g., the Internet, anintranet, a local area network, a mobile communications network, or thelike). In some embodiments, network interface 406 can include anycombination of any number of a network interface controller (NIC), aradio frequency (RF) module, a transponder, a transceiver, a modem, arouter, a gateway, a wired network adapter, a wireless network adapter,a Bluetooth adapter, an infrared adapter, an near-field communication(“NFC”) adapter, a cellular network chip, or the like.

In some embodiments, optionally, apparatus 400 can further includeperipheral interface 408 to provide a connection to one or moreperipheral devices. As shown in FIG. 4 , the peripheral device caninclude, but is not limited to, a cursor control device (e.g., a mouse,a touchpad, or a touchscreen), a keyboard, a display (e.g., acathode-ray tube display, a liquid crystal display, or a light-emittingdiode display), a video input device (e.g., a camera or an inputinterface coupled to a video archive), or the like.

It should be noted that video codecs (e.g., a codec performing process200A, 200B, 300A, or 300B) can be implemented as any combination of anysoftware or hardware modules in apparatus 400. For example, some or allstages of process 200A, 200B, 300A, or 300B can be implemented as one ormore software modules of apparatus 400, such as program instructionsthat can be loaded into memory 404. For another example, some or allstages of process 200A, 200B, 300A, or 300B can be implemented as one ormore hardware modules of apparatus 400, such as a specialized dataprocessing circuit (e.g., an FPGA, an ASIC, an NPU, or the like).

In VVC, a picture is divided into one or more tile rows and one or moretile columns. A tile is a sequence of CTUs that covers a rectangularregion of a picture. The CTUs in a tile are scanned in raster scan orderwithin that tile. A slice consists of an integer number of completetiles or an integer number of consecutive complete CTU rows within atile of a picture. Consequently, each vertical slice boundary is also avertical tile boundary. It is possible that a horizontal boundary of aslice is not a tile boundary but consists of horizontal CTU boundarieswithin a tile. This occurs when a tile is split into multiplerectangular slices, each of which consists of an integer number ofconsecutive complete CTU rows within the tile.

In VVC, a coded video bitstream which is a sequence of bits in form ofnetwork abstraction layer (NAL) unit or byte stream forms one or morecoded video sequences (CVS), and each CVS consists of one or more codedlayer video sequences (CLVS). A CLVS is a sequence of picture units(PUs) and each PU contains exactly one coded picture.

A PU consists of zero or one picture header (PH) NAL unit which containspicture header syntax structure as payload, one coded picture whichcomprises one or more video coding layer (VCL) NAL units, and zero ormore other non-VCL NAL units. A VCL NAL unit contains a coded slicewhich consists of slice header and slice data

In VVC, a range of quantization parameter (QP) can be from 0 to 63, andthe signaling of initial QP can be changed accordingly. The initialvalue of SliceQpY is modified at the slice level when a non-zero valueof slice_qp_delta is coded in the slice header. Specifically, the valueof init_qp_minus26 is modified to be in the range of (−26+QpBdOffsetY)to +37. When the size of a transform block is not a power of 4, thetransform coefficients are processed along with a modification to the QPor QP levelScale table rather than by multiplication by 181/256 (or181/128), to compensate for an implicit scaling by the transformprocess. For transform skip blocks, minimum allowed QP is defined as 4because quantization step size becomes 1 when QP is equal to 4.

In addition, QP value may be changed from one CU to another CU or fromone quantization group to another quantization group. Delta QP valuesfor luma and chroma components can be signaled separately.

For each luma coding block, first, a variable qP_(Y_PREV) is derived asfollows:

-   -   If one or more of the following conditions are true, qP_(Y_PREV)        is set equal to SliceQp_(Y):        -   The current quantization group is the first quantization            group in a slice.        -   The current quantization group is the first quantization            group in a tile.    -   Otherwise, qP_(Y_PREV) is set equal to the luma quantization        parameter Qp_(Y) of the last luma coding unit in the previous        quantization group in decoding order.

Second, a variable qP_(Y_A) is derived as follows:

-   -   If one or more of the following conditions are true, qP_(Y_A) is        set equal to qP_(Y_PREV):        -   the left neighboring block of the current quantization group            is unavailable.        -   the left neighboring block of the current quantization group            and the current coding block are in the different coding            tree block (CTB)    -   Otherwise, qP_(Y_A) is set equal to the luma quantization        parameter of the coding unit on the upper side of the current        quantization group.

Third, the variable qP_(Y_B) is derived as follows:

-   -   If one or more of the following conditions are true, qP_(Y_B) is        set equal to qP_(Y_PREV):        -   the upper neighboring block of the current quantization            group is unavailable.        -   the upper neighboring block of the current quantization            group and the current coding block are in the different            coding tree block (CTB)    -   Otherwise, qP_(Y_B) is set equal to the luma quantization        parameter of the coding unit on the left side of the current        quantization group.

Fourth, if the current quantization group is the first quantizationgroup in a coding tree block (CTB) row within a brick and the upperneighboring block of the current quantization group is available,

qPY_PRED is set to qPY_B

else

qPY_PRED=(qPY_A+qPY_B+1)>>1

After deriving qPY_PRED, quantization parameter of the current lumacoding block Qp′_(Y) can be derived using below Equation 1:

Qp′_(Y)=((qPY_PRED+CuQpDeltaVal+64+2*QpBdOffsetY)%(64+QpBdOffsetY))  (Eq.1)

where QpBdOffsetY is equal to 6*sps_bitdepth_minus8, and the variableCuQpDeltaVal specifies the difference between the quantization parameterof a the luma coding block and its prediction value.

In VVC, CuQpDeltaVal is specified ascu_qp_delta_abs*(1−2*cu_qp_delta_sign_flag), where cu_qp_delta_abs andcu_qp_delta_sign_flag are syntax elements signaled in the bitstream atCU level. When cu_qp_delta_abs and cu_qp_delta_sign_flag are not presentin the bitstream, CuQpDeltaVal can be inferred to be 0.

The quantization parameter for chroma coding block may be different fromQp_(Y). The offset between a chroma quantization parameter (Qp_(Cb),Qp_(Cr),Qp_(CbCr)) and a luma quantization parameter may be signaled inthe bitstream. In VVC, chroma quantization parameters Qp′_(Cb) andQp′_(Cr), and the QP for joint Cb-Cr coding Qp′_(CbCr) can be derivedusing the following Equations 2-4:

QP_(Cb)′=Clip3(−QpBdOffset_(C),63,qP_(Cb)+pps_cb_qp_offset+slice_cb_qp_offset+CuQpOffset_(Cb))+QpBdOffset_(c)  (Eq.2)

Qp_(Cr)′=Clip3(−QpBdOffset_(C),63,qP_(Cr)+pps_cr_qp_offset+slice_cr_qp_offset+CuQpOffset_(Cr))+QpBdOffset_(c)  (Eq.3)

QP_(CbCr)′=Clip3(−QpBdOffset_(C),63,qP_(CbCr)+pps_cbcr_qp_offset+slice_cbcr_qp_offset+CuQpOffset_(CbCr))+QpBdOffset_(c)  (Eq.4)

where qP_(Cb), qP_(Cr), and qP_(CbCr) can be derived from a look-uptable with input of clipped value of Qp_(Y) using Equations 5-8:

qPi_(Chroma)=Clip3(−QpBdOffset,63,Qp_(Y)−QpBdOffset)  (Eq. 5)

qP_(Cb)=ChromaQpTable[0][qP_(Chroma)]  (Eq. 6)

qP_(Cr)ChromaQpTable[1][qP_(Chroma)]  (Eq. 7)

qP_(CbCr)=ChromaQpTable[2][qP_(Chroma)]  (Eq. 8)

CuQpOffset_(Cb) CuQpOffset_(Cr) and CuQpOffset_(CbCr) are set to 0 whencu_chroma_qp_offset_flag is equal to 0; and can be derived usingEquations 9-11 when cu_chroma_qp_offset_flag is equal to 1:

CuQpOffset_(Cb)=cb_qp_offset_list[cu_chroma_qp_offset_idx]  (Eq. 9)

CuQpOffset_(Cr)=cr_qp_offset_list[cu_chroma_qp_offset_idx]  (Eq. 10)

CuQpOffset_(CbCr)=joint_cbcr_qp_offset_list[cu_chroma_qp_offset_idx]  (Eq.11)

where cu_chroma_qp_offset_flag and cu_chroma_qp_offset_idx are syntaxelements signaled in the bitstream.

As discussed above, cu_qp_delta_abs and cu_qp_delta_sign_flag aresignaled to derive CuQpDeltaVal, which can be used for QP derivation.cu_chroma_qp_offset_flag, cu_chroma_qp_offset_idx, cb_qp_offset_list[i],cr_qp_offset_list[i], and joint_cbcr_qp_offset_list[i] are signaled toderive CuQpOffset_(Cb), CuQpOffset_(Cr) and CuQpOffset_(CbCr), which canbe used for chroma QP derivation.

Below is an introduction of the related syntax signaling process. First,cu_qp_delta_enabled_flag, cu_qp_delta_subdiv,cu_chroma_qp_offset_enabled_flag, and cu_chroma_qp_offset_subdiv can besignaled in the picture parameter set (PPS) as shown in FIG. 5 , whichillustrates exemplary PPS syntax for CU delta QP.

After that, variables IsCuQpDeltaCoded and IsCuChromaQpOffsetCoded, theposition of quantization parameter group, and variables qgOnY and qgOnCcan be derived at coding tree level as shown in FIG. 6 , whichillustrates exemplary codingt tree syntax for CU delta QP.

Further, cu_qp_delta_abs/cu_qp_delta_sign_flag andcu_chroma_qp_offset_flag/cu_chroma_qp_offset_idx are signaled attransform unit conditioned upon IsCuQpDeltaCoded andIsCuChromaQpOffsetCoded being derived at the coding unit level, as shownin FIG. 7 , which illustrates exemplary transform unit level syntax forCU delta QP.

In the example shown in FIG. 5 , cu_qp_delta_subdiv specifies themaximum cbSubdiv value of coding units that convey cu_qp_delta_abs andcu_qp_delta_sign_flag, and cu_chroma_qp_offset_subdiv specifies themaximum cbSubdiv value of coding units that conveycu_chroma_qp_offset_flag. cbSubdiv is a variable of which the value isrelated to the size of a coding unit. A smaller coding unit has a largervalue of cbSubdiv. With the partitioning of a coding unit into multiplesub-coding units, the value of cbSudiv increases. The value range ofcu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv are dependent on avariable referred to as MaxMttDepthY, which is derived on slice leveland slice type.

MaxMttDepthY=slice_max_mtt_hierarchy_depth_luma  (Eq. 12)

where slice_max_mtt_hierarchy_depth_luma is signaled in slice header asshown in FIG. 8 , which illustrates exemplary slice header syntax.

As described above, to determine the maximum depth of the coding unitwhich may convey cu_qp_delta_abs/cu_qp_delta_sign_flag andcu_chroma_qp_offset_flag, two syntax elements cu_qp_delta_subdiv andcu_chroma_qp_offset_subdiv are signaled in the PPS level. However, thevalue ranges of cu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv dependon a variable MaxMttDepthY, which is derived on slice level and the typeof the slice. Thus, a PPS level syntax element depends on slice levelsyntax.

In the bitstream syntax structure, PPS is at a higher level than theslice level, and the syntax of PPS comes before slice syntax. For adecoder, the value of higher level syntax can be referenced when parsinglower level syntax. However, the value of lower level syntax cannot bereferenced when parsing higher level syntax. Therefore, in the currentVVC techniques, that the cu_qp_delta_subdiv andcu_chroma_qp_offset_subdiv depend on slice header syntax creates alogical issue which needs to be solved.

To address the above described problems, solutions are provided in thevarious embodiments of the present disclosure. In some embodiments,cu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv can be moved to sliceheader after slice_max_mtt_hierarchy_depth_luma is signaled. That way,cu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv are no longer PPSlevel syntax elements. One example of slice header syntax is shown inFIG. 9 (e.g., element 901).

In the example shown in FIG. 9 , cu_qp_delta_enabled_flag andcu_chroma_qp_offset_enabled_flag are signaled in PPS. In someembodiments, cu_qp_delta_enabled_flag andcu_chroma_qp_offset_enabled_flag can be signaled in the slice header, asshown in FIG. 10 (e.g., element 1001).

In the example shown in FIG. 10 , the range of cu_qp_delta_subdiv andcu_chroma_qp_offset_subdiv can be determined as follows. For example,the value range of cu_qp_delta_subdiv can be specified as follows. Ifslice_type is equal to I, the value of cu_qp_delta_subdiv is in therange of 0 to 2*(CtbLog2SizeY−MinQtLog2SizeIntraY+MaxMttDepthY),inclusive. Otherwise (slice_type is not equal to I), the value ofcu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+MaxMttDepthY), inclusive. When notpresent, the value of cu_qp_delta_subdiv can be inferred to be equal to0.

The value range of cu_chroma_qp_offset_subdiv can be specified asfollows. If slice_type is equal to I, the value ofcu_chroma_qp_offset_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeIntraY+MaxMttDepthY), inclusive. Otherwise(slice_type is not equal to I), the value of cu_chroma_qp_offset_subdivis in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+MaxMttDepthY), inclusive. When notpresent, the value of cu_chroma_qp_offset_subdiv can be inferred to beequal to 0.

In some embodiments, cu_qp_delta_subdiv and cu_chroma_qp_offset_subdivare moved to picture header and at the same time syntax elements whichare used to derive MaxMttDepthY are also moved to picture header, sothat the range of cu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv arenot dependent on slice level syntax.

Since one picture may contain multiple slices with different slice typesof inter and intra. Thus, in this embodiment, cu_qp_delta_subdiv is aresplit into two syntax elements, namely ph_cu_qp_delta_subdiv_intra_sliceand ph_cu_qp_delta_subdiv_inter_slice. cu_chroma_qp_offset_subdiv issplit into two syntax elements, namelyph_cu_chroma_qp_offset_subdiv_intra_slice andph_cu_chroma_qp_offset_subdiv_inter_slice.ph_cu_qp_delta_subdiv_intra_slice andph_cu_chroma_qp_offset_subdiv_intra_slice are for intra slice in thecurrent picture and ph_cu_qp_delta_subdiv_inter_slice andph_cu_chroma_qp_offset_subdiv_inter_slice are for inter slice in thecurrent picture. Similarly, two syntax elements are signaled forMaxMttDepthY of intra slice and inter slice, namelyph_max_mtt_hierarchy_depth_intra_slice_luma andph_max_mtt_hierarchy_depth_inter_slice.

An example of picture header syntax is shown in Table 11 of FIG. 11 . Asshown in Table 11, ph_cu_qp_delta_subdiv_intra_slice (e.g., element1101), ph_cu_chroma_qp_offset_subdiv_intra_slice (e.g., element 1102),ph_cu_qp_delta_subdiv_inter_slice (e.g., element 1103), andph_cu_chroma_qp_offset_subdiv_inter_slice (e.g., element 1104) are shownin italics and grey.

For an intra slice, ph_cu_qp_delta_subdiv_intra_slice specifies themaximum cbSubdiv value of coding units in the intra slice that conveycu_qp_delta_abs and cu_qp_delta_sign_flag. The value ofph_cu_qp_delta_subdiv_intra_slice is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeIntraY+ph_max_mtt_hierarchy_depth_intra_slice_luma),inclusive. When not present, the value ofph_cu_qp_delta_subdiv_intra_slice can be inferred to be equal to 0.

ph_cu_chroma_qp_offset_subdiv_intra_slice specifies the maximum cbSubdivvalue of coding units in the intra slice that conveycu_chroma_qp_offset_flag. The value ofph_cu_chroma_qp_offset_subdiv_intra_slice is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeIntraY+ph_max_mtt_hierarchy_depth_intra_slice_luma),inclusive. When not present, the value ofph_cu_chroma_qp_offset_subdiv_intra_slice can be inferred to be equal to0.

In the disclosed embodiments,ph_max_mtt_hierarchy_depth_intra_slice_luma is signaled in pictureheader, and specifies a maximum hierarchy depth for coding unitsresulting from multi-type tree splitting of a quadtree leaf in sliceswith sh_slice_type equal to “I” (i.e., intra-prediction slice).CtbLog2SizeY and MinQtLog2SizeIntraY are derived using the followingEquations 13-15, in which CtbLog2SizY represents a size of a luma codingtree block of a coding tree unit in slices with slice_type equal to “I”(i.e., intra-prediction slice), and MinQtLog2SizeIntraY represents aminimum size in luma samples of a luma leaf block resulting fromquadtree splitting of the coding tree unit in the slices with slice_typeequal to “I.”

CtbLog2SizeY=sps_log2_ctu_size_minus5+5  (Eq. 13)

MinQtLog2SizeIntraY=sps_log2_diff_min_qt_min_cb_intra_slice_luma+MinCbLog2SizeY  (Eq. 14)

MinCbLog2SizeY=sps_log2_min_luma_coding_block_size_minus2+2  (Eq. 15)

sps_log2_ctu_size_minus5, sps_log2_diff_min_qt_min_cb_intra_slice_luma,and sps_log2_min_luma_coding_block_size_minus2 are syntax elementssignaled in SPS.

The variable CuQpDeltaSubdiv is derived as the maximum cbSubdiv value ofcoding units that convey cu_qp_delta_abs and cu_qp_delta_sign_flag, andthe variable CuChromaQpOffsetSubdiv is derived as the maximum cbSubdivvalue of coding units that convey cu_chroma_qp_offset_flag. These twovariables are derived as Eq. 16 and Eq. 17, respectively.

CuQpDeltaSubdiv=ph_cu_qp_delta_subdiv_intra_slice  (Eq. 16)

CuChromaQpOffsetSubdiv=ph_cu_chroma_qp_offset_subdiv_intra_slice  (Eq.17)

For an inter slice, ph_cu_qp_delta_subdiv_inter_slice specifies themaximum cbSubdiv value of coding units that in inter slice conveycu_qp_delta_abs and cu_qp_delta_sign_flag. The value ofph_cu_qp_delta_subdiv_inter_slice may be in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+ph_max_mtt_hierarchy_depth_inter_slice),inclusive. When not present, the value ofph_cu_qp_delta_subdiv_inter_slice can be inferred to be equal to 0.ph_cu_chroma_qp_offset_subdiv_inter_slice specifies the maximum cbSubdivvalue of coding units in the inter slice that conveycu_chroma_qp_offset_flag. The value ofph_cu_chroma_qp_offset_subdiv_inter_slice is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+ph_max_mtt_hierarchy_depth_inter_slice),inclusive. When not present, the value ofph_cu_chroma_qp_offset_subdiv_inter_slice can be inferred to be equal to0.

ph_max_mtt_hierarchy_depth_inter_slice can be signaled in pictureheader, and specifies a maximum hierarchy depth for coding unitsresulting from multi-type tree splitting of a quadtree leaf in sliceswith sh_slice_type not equal to “I” (i.e., inter-prediction slice withslice_type equal to “P” or “B”). CtbLog2SizY and MinQtLog2SizeInterY arederived using the following Equations 18-20, in which CtbLog2SizYrepresents a size of a luma coding tree block of a coding tree unit inslices with slice_type not equal to “I” (i.e., inter-prediction slicewith slice_type equal to “P” or “B”), and MinQtLog2SizeInterY representsa minimum size in luma samples of a luma leaf block resulting fromquadtree splitting of the coding tree unit in the slices with slice_typenot equal to “I.”

CtbLog2SizeY=sps_log2ctu_size_minus5+5  (Eq. 18)

MinQtLog2SizeInterY=sps_log2_diff_min_qt_min_cb_inter_slice_luma+MinCbLog2SizeY  (Eq.19)

MinCbLog2SizeY=sps_log2_min_luma_coding_block_size_minus2+2  (Eq. 20)

sps_log2_ctu_size_minus5, sps_log2_diff_min_qt_min_cb_inter_slice_luma,and sps_log2_min_luma_coding_block_size_minus2 are syntax elementssignaled in SPS.

The variable CuQpDeltaSubdiv is derived as the maximum cbSubdiv value ofcoding units that convey cu_qp_delta_abs and cu_qp_delta_sign_flag andthe variable CuChromaQpOffsetSubdi is derived as the maximum cbSubdivvalue of coding units that convey cu_chroma_qp_offset_flag. These twovariables are derived as Eq. 21 and Eq. 22, respectively.

CuQpDeltaSubdiv=ph_cu_qp_delta_subdiv_inter_slice  (Eq. 21)

CuChromaQpOffsetSubdiv=ph_cu_chroma_qp_offset_subdiv_inter_slice  (Eq.22)

In some embodiments, cu_qp_delta_subdiv and cu_chroma_qp_offset_subdivcan be signaled both at the PPS level and in the slice header. Forexample, in PPS syntax, pps_cu_qp_delta_subdiv andpps_cu_chroma_qp_offset_subdiv are signaled, as shown in FIG. 12 (e.g.,elements 1201 and 1202). In the slice header, slice_cu_qp_delta_subdivand slice_cu_chroma_qp_offset_subdiv are also signaled, as shown in FIG.13 (e.g., element 1301).

In some embodiments, the range of pps_cu_qp_delta_subdiv andpps_cu_chroma_qp_offset_subdiv depend on the syntax of sequenceparameter set (SPS), as illustrated in the following example. In thisexample, the value range of pps_cu_qp_delta_subdiv is specified asfollows: the value of pps_cu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeY+SpsMaxMttDepthY), inclusive. When notpresent, the value of pps_cu_qp_delta_subdiv can be inferred to be equalto 0. The value range of pps_cu_chroma_qp_offset_subdiv is specified asfollows: the value of pps_cu_chroma_qp_offset_subdiv may be in the rangeof 0 to 2*(CtbLog2SizeY−MinQtLog2SizeY+SpsMaxMttDepthY), inclusive. Whennot present, the value of pps_cu_chroma_qp_offset_subdiv can be inferredto be equal to 0.

In the case where ctbLog2SizeY is defined, MinQtLog2SizeY andSpsMaxMttDepthY can be derived as follows.

In one way, MinQtLog2SizeY can be derived as:

min(MinQtLog2SizeIntraY,MinQtLog2SizeInterY)

or

max(MinQtLog2SizeIntraY,MinQtLog2SizeInterY)

It is appreciated that MinQtLog2SizeIntraY and MinQtLog2SizeIntraY canbe derived using various techniques, such as those defined in VVC draft6.

In an alternative way, the value of MinQtLog2SizeY can be derived basedon the following Equation 23:

MinQtLog2SizeY=sps_log2_diff_min_qt_min_cb_luma+MinCbLog2SizeY  (Eq. 23)

Where sps_log2_diff_min_qt_min_cb_luma is signaled in SPS as shown inFIG. 14 (e.g., element 1401). It is appreciated that MinCbLog2SizeY canbe derived using various techniques, such as those defined in VVC draft6.

With respect to SpsMaxMttDepth, in one way, SpsMaxMttDepthY can bederived as:

min(sps_max_mtt_hierarchy_depth_intra_slice_luma,sps_max_mtt_hierarchy_depth_inter_slice)

or

max(sps_max_mtt_hierarchy_depth_intra_slice_luma,sps_max_mtt_hierarchy_depth_inter_slice)

where sps_max_mtt_hierarchy_depth_intra_slice_luma andsps_max_mtt_hierarchy_depth_inter_slice can be signaled in SPS.

In an alternative way, the value of SpsMaxMttDepthY can be derived as:

SpsMaxMttDepthY=sps_max_mtt_depth_luma  (Eq. 24)

where sps_max_mtt_depth_luma can be signaled in SPS, as shown in FIG. 14(e.g., element 1402).

In the above example, PPS syntax elements pps_cu_qp_delta_subdiv andpps_cu_chroma_qp_offset_subdiv depend on SPS syntax. Such parsingdependency between PPS and SPS may not be desirable. In order to addressthis dependency issue, in some embodiments, the value range ofpps_cu_qp_delta_subdiv can be specified as follows.

The value of pps_cu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeY+ppsMaxMttDepthY), inclusive. When notpresent, the value of pps_cu_qp_delta_subdiv can be inferred to be equalto 0.

The value range of pps_cu_chroma_qp_offset_subdiv can be specified asfollows. The value of pps_cu_chroma_qp_offset_subdiv is in the range of0 to 2*(CtbLog2SizeY−MinQtLog2SizeY+ppsMaxMttDepthY), inclusive. Whennot present, the value of pps_cu_chroma_qp_offset_subdiv can be inferredto be equal to 0.

CtbLog2SizeY, MinQtLog2SizeY, and ppsMaxMttDepthY are derived asfollows:

CtbLog2SizeY=pps_log2_ctb_size  (Eq. 25)

MinQtLog2SizeY=pps_log2_min_qt  (Eq. 26)

ppsMaxMttDepthY=pps_max_mtt_depth_luma  (Eq. 27)

pps_log2_ctb_size, pps_log2_min_qt and pps_max_mtt_depth_luma can besignaled in PPS, as shown in FIG. 15 (e.g., element 1501).

In the above examples, the range of slice_cu_qp_delta_subdiv andslice_cu_chroma_qp_offset_subdiv depend on the syntax of the sliceheader. For example, the value range of slice_cu_qp_delta_subdiv can bespecified as follows. If slice_type is equal to I, the value ofslice_cu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeIntraY+SliceMaxMttDepthY), inclusive.Otherwise (slice_type is not equal to I), the value ofslice_cu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+SliceMaxMttDepthY), inclusive. Whennot present, the value of slice_cu_qp_delta_subdiv can be inferred to beequal to 0 or pps_cu_qp_delta_subdiv.

And the value range of slice_cu_chroma_qp_offset_subdiv can be specifiedas follows. If slice_type is equal to I, the value ofslice_cu_chroma_qp_offset_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeIntraY+SliceMaxMttDepthY), inclusive.Otherwise (slice_type is not equal to I), the value ofslice_cu_chroma_qp_offset_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+SliceMaxMttDepthY), inclusive. Whennot present, the value of slice_cu_chroma_qp_offset_subdiv can beinferred to be equal to 0 or pps_cu_chroma_qp_offset_subdiv.

In cases where CtbLog2SizeY, MinQtLog2SizeIntraY and MinQtLog2SizeInterYare defined, SliceMaxMttDepthY can be derived as:

SliceMaxMttDepthY=slice_max_mtt_hierarchy_depth_luma  (Eq. 28)

slice_max_mtt_hierarchy_depth_luma can be signaled in the slice header.

In the above examples, cu_qp_delta_subdiv can be inferred to beslice_cu_qp_delta_subdiv. Alternatively, cu_qp_delta_subdiv can beinferred to be pps_cu_qp_delta_subdiv first; then ifslice_cu_qp_delta_subdiv is present, slice_cu_qp_delta_subdiv overridesand cu_qp_delta_subdiv can be inferred to be slice_cu_qp_delta_subdiv.The value of cu_qp_delta_subdiv can be used to derive Qp_(Y).

Further, cu_chroma_qp_offset_subdiv can be inferred to beslice_cu_chroma_qp_offset_subdiv. Alternatively,cu_chroma_qp_offset_subdiv can be inferred to bepps_cu_chroma_qp_offset_subdiv first; then ifslice_cu_chroma_qp_offset_subdiv is present,slice_cu_chroma_qp_offset_subdiv overrides andcu_chroma_qp_offset_subdiv can be inferred to beslice_cu_chroma_qp_offset_subdiv. The value ofcu_chroma_qp_offset_subdiv can be used to derive Qp_(Cb), Qp_(Cr),QP_(CbCr).

In some embodiments, cu_qp_delta_subdiv and cu_chroma_qp_offset_subdivcan be signaled both at the SPS level and in the slice header. In SPS,sps_cu_qp_delta_subdiv and sps_cu_chroma_qp_offset_subdiv can besignaled as shown in FIG. 16 (e.g., element 1601); and in the sliceheader, slice_cu_qp_delta_subdiv and slice_cu_chroma_qp_offset_subdivare signaled as shown in FIG. 17 (e.g., element 1701).

In some embodiments, the range of sps_cu_qp_delta_subdiv andsps_cu_chroma_qp_offset_subdiv depend on the syntax of SPS. For example,the value range of sps_cu_qp_delta_subdiv can be specified as follows.The value of sps_cu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeY+SpsMaxMttDepthY), inclusive. When notpresent, the value of sps_cu_qp_delta_subdiv can be inferred to be equalto 0. And the value range of sps_cu_chroma_qp_offset_subdiv is specifiedas follows. The value of sps_cu_chroma_qp_offset_subdiv is in the rangeof 0 to 2*(CtbLog2SizeY−MinQtLog2SizeY+SpsMaxMttDepthY), inclusive. Whennot present, the value of sps_cu_chroma_qp_offset_subdiv can be inferredto be equal to 0.

In cases where ctbLog2SizeY is defined, MinQtLog2SizeY andSpsMaxMttDepthY can be derived as follows.

In one way, MinQtLog2SizeY can be derived as:

min(MinQtLog2SizeIntraY,MinQtLog2SizeInterY)

or

max(MinQtLog2SizeIntraY,MinQtLog2SizeInterY)

Where MinQtLog2SizeIntraY and MinQtLog2SizeIntraY can be derived usingvarious techniques, such as those defined in VVC draft 6.

In an alternative way, the value of MinQtLog2SizeY can be derived usingEquation 29 below.

MinQtLog2SizeY=sps_log2_diff_min_qt_min_cb_luma+MinCbLog2SizeY  (Eq. 29)

sps_log2_diff_min_qt_min_cb_luma can be signaled in SPS as shown in FIG.18 (e.g., element 1801). It is appreciated that MinCbLog2SizeY can bederived using various techniques, such as those defined in VVC draft 6.

With respect to SpsMaxMttDepthY, in one way, SpsMaxMttDepthY can bederived as:

min(sps_max_mtt_hierarchy_depth_intra_slice_luma,sps_max_mtt_hierarchy_depth_inter_slice)

or

max(sps_max_mtt_hierarchy_depth_intra_slice_luma,sps_max_mtt_hierarchy_depth_inter_slice)

sps_max_mtt_hierarchy_depth_intra_slice_luma andsps_max_mtt_hierarchy_depth_inter_slice can be signaled in SPS.

In an alternative way, SpsMaxMttDepthY can be derived as:

SpsMaxMttDepthY=sps_max_mtt_depth_luma  (Eq. 30)

sps_max_mtt_depth_luma can be signaled in SPS, as shown in FIG. 18(e.g., element 1802).

Further, in the above examples, the range of slice_cu_qp_delta_subdivand slice_cu_chroma_qp_offset_subdiv depend on the syntax of the sliceheader. For example, the value range of slice_cu_qp_delta_subdiv can bespecified as follows. If slice_type is equal to I, the value ofslice_cu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeIntraY+SliceMaxMttDepthY), inclusive.Otherwise(slice_type is not equal to I), the value ofslice_cu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+SliceMaxMttDepthY), inclusive. Whennot present, the value of slice_cu_qp_delta_subdiv can be inferred to beequal to 0 or sps_cu_qp_delta_subdiv.

The value range of slice_cu_chroma_qp_offset_subdiv can be specified asfollows. If slice_type is equal to I, the value ofslice_cu_chroma_qp_offset_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeIntraY+SliceMaxMttDepthY), inclusive.Otherwise (slice_type is not equal to I), the value ofslice_cu_chroma_qp_offset_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+SliceMaxMttDepthY), inclusive. Whennot present, the value of slice_cu_chroma_qp_offset_subdiv can beinferred to be equal to 0 or sps_cu_chroma_qp_offset_subdiv.

In cases where CtbLog2SizeY, MinQtLog2SizeIntraY and MinQtLog2SizeInterYare defined, SliceMaxMttDepthY can be derived as:

SliceMaxMttDepthY=slice_max_mtt_hierarchy_depth_luma  (Eq. 31)

slice_max_mtt_hierarchy_depth_luma can be signaled in the slice header.

In the above examples, cu_qp_delta_subdiv can be inferred to beslice_cu_qp_delta_subdiv. Alternatively, cu_qp_delta_subdiv can beinferred to be sps_cu_qp_delta_subdiv first; then ifslice_cu_qp_delta_subdiv is present, slice_cu_qp_delta_subdiv overridesand cu_qp_delta_subdiv can be inferred to be slice_cu_qp_delta_subdiv.Cu_qp_delta_subdiv can be used to derive Qp_(Y).

Further, in the above examples, cu_chroma_qp_offset_subdiv can beinferred to be slice_cu_chroma_qp_offset_subdiv. Alternatively,cu_chroma_qp_offset_subdiv can be inferred to besps_cu_chroma_qp_offset_subdiv first; then ifslice_cu_chroma_qp_offset_subdiv is present,slice_cu_chroma_qp_offset_subdiv overrides andcu_chroma_qp_offset_subdiv can be inferred to beslice_cu_chroma_qp_offset_subdiv. Cu_chroma_qp_offset_subdiv can be usedto derive Qp_(Cb), Qp_(Cr), QP_(CbCr).

In some embodiments, the syntax of cu_qp_delta_subdiv andcu_chroma_qp_offset_subdiv can be signaled at PPS level. However, therange restriction of cu_qp_delta_subdiv and cu_chroma_qp_offset_subdivcan be changed so that they are not dependent on slice syntax.

As an example, cu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv can besignaled in PPS as shown in FIG. 5 . The value range ofcu_qp_delta_subdiv can be specified as follows. The value ofcu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeY+MaxMttDepthY), inclusive. When notpresent, the value of cu_qp_delta_subdiv can be inferred to be equal to0. The value range of cu_chroma_qp_offset_subdiv can be specified asfollows. The value of cu_chroma_qp_offset_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeY+MaxMttDepthY), inclusive. When notpresent, the value of cu_chroma_qp_offset_subdiv can be inferred to beequal to 0.

In cases where ctbLog2SizeY is defined, MinQtLog2SizeY and MaxMttDepthYcan be inferred on SPS level. For example, MaxMttDepthY can be derivedas:

min(sps_max_mtt_hierarchy_depth_intra_slice_luma,sps_max_mtt_hierarchy_depth_inter_slice)

or

max(sps_max_mtt_hierarchy_depth_intra_slice_luma,sps_max_mtt_hierarchy_depth_inter_slice)

sps_max_mtt_hierarchy_depth_intra_slice_luma andsps_max_mtt_hierarchy_depth_inter_slice can be signaled in SPS.

In an alternative way, MaxMttDepthY can be derived as:

MaxMttDepthY=sps_max_mtt_depth_luma

sps_max_mtt_depth_luma can be signaled in SPS, as shown in FIG. 19(e.g., element 1901).

In one way, MinQtLog2SizeY can be derived as:

min(MinQtLog2SizeIntraY,MinQtLog2SizeInterY)

or

max(MinQtLog2SizeIntraY,MinQtLog2SizeInterY)

It is appreciated that MinQtLog2SizeIntraY and MinQtLog2SizeIntraY canbe derived using various techniques, such as those defined in VVC draft6.

In an alternative way, the value of MinQtLog2SizeY can be derived basedon the following Equation 32:

MinQtLog2SizeY=sps_log2_diff_min_qt_min_cb_luma+MinCbLog2SizeY  (Eq. 32)

sps_log2_diff_min_qt_min_cb_luma is signaled in SPS as shown in FIG. 13(e.g., element 1301). It is appreciated that MinCbLog2SizeY can bederived using various techniques, such as those defined in VVC draft 6.

Based on the above example, the range of cu_qp_delta_subdiv andcu_chroma_qp_offset_subdiv are not overridden at the slice header level.

In some embodiments, cu_qp_delta_subdiv and cu_chroma_qp_offset_subdivcan be signaled at PPS level. However, the range restriction ofcu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv can be fixed so thatthey are not dependent on slice syntax.

For example, cu_qp_delta_subdiv and cu_chroma_qp_offset_subdiv can besignaled in PPS as shown in FIG. 5 . The value range ofcu_qp_delta_subdiv can be specified as follows. the value ofcu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeY+MaxMttDepthY), inclusive. When notpresent, the value of cu_qp_delta_subdiv can be inferred to be equal to0. And the value range of cu_chroma_qp_offset_subdiv is specified asfollows. The value of cu_chroma_qp_offset_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeY+MaxMttDepthY), inclusive. When notpresent, the value of cu_chroma_qp_offset_subdiv can be inferred to beequal to 0.

Where CtbLog2SizeY, MinQtLog2SizeY and MaxMttDepthY can be derived inthe following manners: CtbLog2SizeY/MinQtLog2SizeY/MaxMttDepthY can bespecified by profile; or CtbLog2SizeY/MinQtLog2SizeY/MaxMttDepthY can bea fixed number value.

Based on the above example, the range of cu_qp_delta_subdiv andcu_chroma_qp_offset_subdiv are not overridden at the slice header level.

In some embodiments, cu_qp_delta_subdiv and cu_chroma_qp_offset_subdivcan be signaled in PPS as shown in FIG. 5 . The value range ofcu_qp_delta_subdiv can be specified as follows. The value ofcu_qp_delta_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeY+MaxMttDepthY), inclusive. When notpresent, the value of cu_qp_delta_subdiv can be inferred to be equal to0. And the value range of cu_chroma_qp_offset_subdiv is specified asfollows. The value of cu_chroma_qp_offset_subdiv is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeY+MaxMttDepthY), inclusive. When notpresent, the value of cu_chroma_qp_offset_subdiv can be inferred to beequal to 0.

CtbLog2SizeY, MinQtLog2SizeY and MaxMttDepthY can be inferred on PPSlevel. For example,

CtbLog2SizeY=pps_log2_ctb_size  (Eq. 33)

MinQtLog2SizeY=pps_log2_min_qt  (Eq. 34)

MaxMttDepthY=pps_max_mtt_depth_luma  (Eq. 35)

pps_log2_ctb_size, pps_log2_min_qt and pps_max_mtt_depth_luma aresignaled in PPS as shown in FIG. 20 (e.g., element 2001).

Based on the above example, the range of cu_qp_delta_subdiv andcu_chroma_qp_offset_subdiv are not overridden at the slice header level.

FIG. 21 is a flowchart of a computer-implemented method 2100 forprocessing video content, consistent with embodiments of the disclosure.

At step 2102, a depth parameter associated with a depth of a codingblock can be received. The depth parameter can be e.g., a variable“MaxMttDepthY” derived from a maximum depth of a multiple-type treehierarchy of a luma block (e.g., “slice_max_mtt_hierarchy_depth_luma”).In some embodiments, “slice_max_mtt_hierarchy_depth_luma” can besignaled in a slice header associated with the coding block.

The coding block can be associated with a slice. The slice may beassociated with intra-prediction or inter prediction. In response to theslice being associated with intra-prediction, the delta QP value or thechroma QP offset value can be determined for the slice associated withintra-prediction. Otherwise, in response to the slice being associatedwith inter-prediction, the delta QP value or the chroma QP offset valuecan be determined for the slice associated with inter-prediction. Forexample, when “slice_type” is equal to “I” which indicates the slice isassociated with intra prediction, the value of “cu_qp_delta_subdiv” isin the range of 0 to 2*(CtbLog2SizeY−MinQtLog2SizeIntraY+MaxMttDepthY),inclusive. Otherwise, when “slice_type” is not equal to “I”, whichindicates the slice is associated with inter prediction, the value of“cu_qp_delta_subdiv” is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+MaxMttDepthY), inclusive. Also as anexample, when “slice_type” is equal to “I”, the value of“cu_chroma_qp_offset_subdiv” is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeIntraY+MaxMttDepthY), inclusive. Otherwisewhen “slice_type” is not equal to “I”, the value of“cu_chroma_qp_offset_subdiv” is in the range of 0 to2*(CtbLog2SizeY−MinQtLog2SizeInterY+MaxMttDepthY), inclusive.

In some embodiments, the depth parameter can be signaled in a pictureheader. It is appreciated that a picture may include a plurality ofslices. For a slice associated with intra-prediction, the correspondingdelta QP value or chroma QP offset value can be determined for the sliceassociated with intra-prediction. For a slice associated withinter-prediction, the corresponding delta QP value or chroma QP offsetvalue can be determined for the slice associated with inter-prediction.For example, as discussed with reference to Table 11 of FIG. 11 ,ph_cu_qp_delta_subdiv_intra_slice andph_cu_chroma_qp_offset_subdiv_intra_slice are signaled in the pictureheader for deriving the delta QP value and the chroma QP offset valuefor a slice associated with intra-prediction. Andph_cu_qp_delta_subdiv_inter_slice andph_cu_chroma_qp_offset_subdiv_inter_slice are signaled in the pictureheader for deriving the delta QP value and the chroma QP offset valuefor a slice associated with inter prediction.

At step 2104, at least one of a delta quantization parameter (QP) valueor a chroma QP offset value can be determined based on the depth of thecoding block. As discussed above, the delta QP value can be determinedbased on “cu_qp_delta_subdiv,” the chroma QP offset value can bedetermined based on “cu_chroma_qp_offset_subdiv,” and“cu_qp_delta_subdiv” and “cu_chroma_qp_offset_subdiv” can be determinedbased on the variable “MaxMttDepthY.”

At step 2106, a luma QP value can be derived based on the determineddelta QP value, and a chroma QP value can be derived based on thedetermined chroma QP offset value.

At step 2108, the coding block can be processed based on the derivedluma QP value and the derived chroma QP value.

In some embodiments, a non-transitory computer-readable storage mediumincluding instructions is also provided, and the instructions may beexecuted by a device (such as the disclosed encoder and decoder), forperforming the above-described methods. Common forms of non-transitorymedia include, for example, a floppy disk, a flexible disk, hard disk,solid state drive, magnetic tape, or any other magnetic data storagemedium, a CD-ROM, any other optical data storage medium, any physicalmedium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROMor any other flash memory, NVRAM, a cache, a register, any other memorychip or cartridge, and networked versions of the same. The device mayinclude one or more processors (CPUs), an input/output interface, anetwork interface, and/or a memory.

The embodiments may further be described using the following clauses:

-   -   1. A computer-implemented method, comprising:    -   receiving a bitstream comprising coded video data;    -   determining a first parameter of a coding block;    -   determining, according to the first parameter, one or more        second parameters associated with a delta quantization parameter        (QP) value or a chroma QP offset value; and    -   determining, according to the one or more second parameters, at        least one of the delta QP value or the chroma QP offset value.    -   2. The method according to clause 1, wherein determining the        first parameter of the coding block comprises:    -   determining if the coding block is associated with an        intra-prediction slice or an inter prediction slice; and    -   in response to the coding block being associated with the        intra-prediction slice, determining the first parameter to be a        parameter associated with the intra-prediction slice, or in        response to the coding block being associated with the        inter-prediction slice, determining the first parameter to be a        parameter associated with the inter-prediction slice.    -   3. The method according to clause 1, wherein the first parameter        is signaled in a slice header associated with the coding block.    -   4. The method according to clause 1, wherein the first parameter        is signaled in a picture header associated with the coding        block.    -   5. The method according to clause 1, further comprising:    -   determining a luma QP value based on the delta QP value;    -   determining a chroma QP value based on the chroma QP offset        value; and    -   processing the coding block based on the luma QP value and the        chroma QP value.    -   6. A system for processing video content, comprising:    -   a memory storing a set of instructions; and    -   at least one processor configured to execute the set of        instructions to cause the system to perform:        -   receiving a bitstream comprising coded video data;        -   determining a first parameter of a coding block;        -   determining, according to the first parameter, one or more            second parameters associated with a delta quantization            parameter (QP) value or a chroma QP offset value; and        -   determining, according to the one or more second parameters,            at least one of the delta QP value or the chroma QP offset            value.    -   7. The system according to clause 6, wherein the at least one        processor is configured to execute the set of instructions to        cause the system to further perform:    -   determining if the coding block is associated with an        intra-prediction slice or an inter prediction slice; and    -   in response to the coding block being associated with the        intra-prediction slice, determining the first parameter to be a        parameter associated with the intra-prediction slice, or in        response to the coding block being associated with the        inter-prediction slice, determining the first parameter to be a        parameter associated with the inter-prediction slice.    -   8. The system according to clause 6, wherein the first parameter        is signaled in a slice header associated with the coding block.    -   9. The system according to clause 6, wherein the first parameter        is signaled in a picture header associated with the coding        block.    -   10. The system according to clause 6, wherein the at least one        processor is configured to execute the set of instructions to        cause the system to further perform:    -   determining a luma QP value based on the delta QP value;    -   determining a chroma QP value based on the chroma QP offset        value; and    -   processing the coding block based on the luma QP value and the        chroma QP value.    -   11. A non-transitory computer readable medium storing        instructions that are executable by at least one processor of a        computer system, wherein the execution of the instructions        causes the computer system to perform a method comprising:    -   receiving a bitstream comprising coded video data;    -   determining a first parameter of a coding block;    -   determining, according to the first parameter, one or more        second parameters associated with a delta quantization parameter        (QP) value or a chroma QP offset value; and    -   determining, according to the one or more second parameters, at        least one of the delta QP value or the chroma QP offset value.    -   12. The non-transitory computer readable medium according to        clause 11, wherein the method further comprises:    -   determining if the coding block is associated with an        intra-prediction slice or an inter prediction slice; and    -   in response to the coding block being associated with the        intra-prediction slice, determining the first parameter to be a        parameter associated with the intra-prediction slice, or in        response to the coding block being associated with the        inter-prediction slice, determining the first parameter to be a        parameter associated with the inter-prediction slice.    -   13. The non-transitory computer readable medium according to        clause 11, wherein the first parameter is signaled in a slice        header associated with the coding block.    -   14. The non-transitory computer readable medium according to        clause 11, wherein the first parameter is signaled in a picture        header associated with the coding block.    -   15. The non-transitory computer readable medium according to        clause 11, wherein the method further comprising:    -   determining a luma QP value based on the delta QP value;    -   determining a chroma QP value based on the chroma QP offset        value; and    -   processing the coding block based on the luma QP value and the        chroma QP value.

It should be noted that, the relational terms herein such as “first” and“second” are used only to differentiate an entity or operation fromanother entity or operation, and do not require or imply any actualrelationship or sequence between these entities or operations. Moreover,the words “comprising,” “having,” “containing,” and “including,” andother similar forms are intended to be equivalent in meaning and be openended in that an item or items following any one of these words is notmeant to be an exhaustive listing of such item or items, or meant to belimited to only the listed item or items.

As used herein, unless specifically stated otherwise, the term “or”encompasses all possible combinations, except where infeasible. Forexample, if it is stated that a database may include A or B, then,unless specifically stated otherwise or infeasible, the database mayinclude A, or B, or A and B. As a second example, if it is stated that adatabase may include A, B, or C, then, unless specifically statedotherwise or infeasible, the database may include A, or B, or C, or Aand B, or A and C, or B and C, or A and B and C.

It is appreciated that the above described embodiments can beimplemented by hardware, or software (program codes), or a combinationof hardware and software. If implemented by software, it may be storedin the above-described computer-readable media. The software, whenexecuted by the processor can perform the disclosed methods. Thecomputing units and other functional units described in this disclosurecan be implemented by hardware, or software, or a combination ofhardware and software. One of ordinary skill in the art will alsounderstand that multiple ones of the above described modules/units maybe combined as one module/unit, and each of the above describedmodules/units may be further divided into a plurality ofsub-modules/sub-units.

In the foregoing specification, embodiments have been described withreference to numerous specific details that can vary from implementationto implementation. Certain adaptations and modifications of thedescribed embodiments can be made. Other embodiments can be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims. It is also intended that the sequence of steps shown in figuresare only for illustrative purposes and are not intended to be limited toany particular sequence of steps. As such, those skilled in the art canappreciate that these steps can be performed in a different order whileimplementing the same method.

In the drawings and specification, there have been disclosed exemplaryembodiments. However, many variations and modifications can be made tothese embodiments. Accordingly, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation.

What is claimed is:
 1. A system for processing video content,comprising: a memory storing a set of instructions; and at least oneprocessor configured to execute the set of instructions to cause thesystem to: receive a data stream comprising coded video data; determinea first parameter of a coding block, wherein at least one of a deltaquantization parameter (QP) value or a chroma QP offset value isdetermined according to the first parameter; and determine, in a sliceheader or a picture header associated with the coding block, a maximumvalue of the first parameter based on a maximum hierarchy depth ofcoding units.
 2. The system according to claim 1, wherein the codingblock is associated with an intra-prediction slice, and the maximumvalue of the first parameter is determined in the slice header accordingto the intra-prediction slice.
 3. The system according to claim 1,wherein the coding block is associated with an inter-prediction sliceand the maximum value of the first parameter is determined in the sliceheader according to the inter-prediction slice.
 4. The system accordingto claim 1, wherein in response to the determination of the maximumvalue of the first parameter in the picture header associated with thecoding block, the at least one processor is configured to execute theset of instructions to cause the system to further: split the maximumvalue of the first parameter into an intra slice element and an interslice element; wherein the intra slice element is for an intra slice,and the inter slice element is for an inter slice.
 5. The systemaccording to claim 1, wherein the at least one processor is configuredto execute the set of instructions to cause the system to further:determine a picture level maximum value of the first parameter;determine the maximum of the first parameter according to the picturelevel maximum value; determine a slice level maximum value of the firstparameter; and determine the maximum of the first parameter to be theslice level maximum value of the first parameter.
 6. The systemaccording to claim 1, wherein the at least one processor is configuredto execute the set of instructions to cause the system to further:determine a luma QP value based on the delta QP value; determine achroma QP value based on the chroma QP offset value; and process thecoding block based on the luma QP value and the chroma QP value.
 7. Thesystem according to claim 1, wherein the first parameter is signaled inat least one of the slice header or the picture header associated withthe coding block.
 8. A computer-implemented method, comprising:receiving a data stream comprising coded video data; determining a firstparameter of a coding block, wherein at least one of a deltaquantization parameter (QP) value or a chroma QP offset value isdetermined according to the first parameter; and determining, in a sliceheader or a picture header associated with the coding block, a maximumvalue of the first parameter based on a maximum hierarchy depth ofcoding units.
 9. The method according to claim 8, wherein the codingblock is associated with an intra-prediction slice, and the maximumvalue of the first parameter is determined in the slice header accordingto the intra-prediction slice.
 10. The method according to claim 8,wherein the coding block is associated with an inter-prediction slice,and the maximum value of the first parameter is determined in the sliceheader according to the inter-prediction slice.
 11. The method accordingto claim 8, further comprising: in response to the determination of themaximum value of the first parameter in the picture header associatedwith the coding block, splitting the maximum value of the firstparameter into an intra slice element and an inter slice element;wherein the intra slice element is for an intra slice, and the interslice element is for an inter slice.
 12. The method according to claim8, wherein determining, in the slice header or the picture headerassociated with the coding block, the maximum value of the firstparameter further comprises: determining a picture level maximum valueof the first parameter; determining the maximum of the first parameteraccording to the picture level maximum value; determining a slice levelmaximum value of the first parameter; and determining the maximum of thefirst parameter to be the slice level maximum value of the firstparameter.
 13. The method according to claim 8, further comprising:determining a luma QP value based on the delta QP value; determining achroma QP value based on the chroma QP offset value; and processing thecoding block based on the luma QP value and the chroma QP value.
 14. Themethod according to claim 8, wherein the first parameter is signaled inat least one of the slice header or the picture header associated withthe coding block.
 15. A non-transitory computer readable medium storinga bitstream of a video for processing according to operationscomprising: determining a first parameter of a coding block, wherein atleast one of a delta quantization parameter (QP) value or a chroma QPoffset value is determined according to the first parameter; anddetermining, in a slice header or a picture header associated with thecoding block, a maximum value of the first parameter based on a maximumhierarchy depth of coding units.
 16. The non-transitory computerreadable medium according to claim 15, wherein the coding block isassociated with an intra-prediction slice, and the maximum value of thefirst parameter is determined in the slice header according to theintra-prediction slice.
 17. The non-transitory computer readable mediumaccording to claim 15, wherein the coding block is associated with aninter-prediction slice, and the maximum value of the first parameter isdetermined in the slice header according to the inter-prediction slice.18. The non-transitory computer readable medium according to claim 15,wherein the operations further comprise: in response to thedetermination of the maximum value of the first parameter in the pictureheader associated with the coding block, splitting the maximum value ofthe first parameter into an intra slice element and an inter sliceelement; wherein the intra slice element is for an intra slice, and theinter slice element is for an inter slice.
 19. The non-transitorycomputer readable medium according to claim 15, wherein the operationsfurther comprise: determining a picture level maximum value of the firstparameter; determining the maximum of the first parameter according tothe picture level maximum value; determining a slice level maximum valueof the first parameter; and determining the maximum of the firstparameter to be the slice level maximum value of the first parameter.20. The non-transitory computer readable medium according to claim 15,wherein the operations further comprise: determining a luma QP valuebased on the delta QP value; determining a chroma QP value based on thechroma QP offset value; and processing the coding block based on theluma QP value and the chroma QP value.